On Fri, Sep 25, 2020 at 06:46:22PM +0000, Tomasz Figa wrote:
+static void *iommu_dma_alloc_noncoherent(struct device *dev, size_t size,
dma_addr_t *handle, enum dma_data_direction dir, gfp_t gfp)+{
- if (!gfpflags_allow_blocking(gfp)) {
struct page *page;page = dma_common_alloc_pages(dev, size, handle, dir, gfp);if (!page)return NULL;return page_address(page);- }
- return iommu_dma_alloc_remap(dev, size, handle, gfp | __GFP_ZERO,
PAGE_KERNEL, 0);iommu_dma_alloc_remap() makes use of the DMA_ATTR_ALLOC_SINGLE_PAGES attribute to optimize the allocations for devices which don't care about how contiguous the backing memory is. Do you think we could add an attrs argument to this function and pass it there?
As ARM is being moved to the common iommu-dma layer as well, we'll probably make use of the argument to support the DMA_ATTR_NO_KERNEL_MAPPING attribute to conserve the vmalloc area.
We could probably at it. However I wonder why this is something the drivers should care about. Isn't this really something that should be a kernel-wide policy for a given system?